I want to learn Adobe Illustrator, need some guide line to start. I am not expert in Photoshop, only know about basics. Is it necessary to learn Photoshop first or can I start directly with Illustrator?

PS and AI use two completely different and UNRELATED approaches to graphics. PS is akin to a mosaic.. moving and paint and image based on lots of tiny tiles ( pixels) AI is a graphic interface for formal based drawings.. you never see the math but its all math... YAY MATH!! Where as in photoshop you will need to keep in mind the ACTUAL dimensions of your images. you can scale vectors (AI) to any size.

in short: PS is for 'photos'. and AI is for 'drawings' .. which one appeals to you.

Adobe has made the interface of both AI and PS very similar. So after you are finish with one you will naturally have a familiarity with the BASICS of the other's interface.

It would be great if you learn the Photoshop first, rather these are not interconnected with each other. photoshop is easy and use for the images, edit them , modify them, or to design the banner. On the other hand illustrator is use to draw vector it's require some mathematic's. it's complex. Both interface are different but if you learn one of them you'll able to learn or study other easily. For learning tutorials this will be helpful to you;vector.tutsplus.creativebloq